1. Field of the Invention
This invention relates to a temperature monitoring device on the inside of matter that is at least partly of water, such as food, the device comprising a temperature sensor.
The invention further relates to an operating process for this device.
The invention relates, in particular, to the temperature monitoring of food, as much during cooking as when in a cold chain.
2. Description of the Related Act
Several of such devices are known of, these devices comprising:                a sensor in contact with the food, capturing thermal data, and        control means for controlling this thermal data, delivering at least some of the thermal data in a form likely to be understood by the user of the device.        
The control means can be laid out so that the user is alerted of an excess in temperature by means of, for example, a light and/or sound warning set off when the sensor detects a temperature in excess of the pre-set temperature threshold, and/or the display of the detected temperature on a display support, such as a LCD screen.
The sensor in these devices comprises in particular:                a food temperature transducer;        connection means to connect with the control means;        an interface circuit between the transducer and the connection means;        an external case that protects the elements that it contains.        
For some of these sensors, the said connection means is wired, such as, for example, those described in the documents U.S. Pat. No. 3,931,620, U.S. Pat. No. 4,309,585 and U.S. 2003 7544.
These wired connections are ergonomically restrictive for the user of such a device, and could notably bear encumbrance and safety problems.
Wireless temperature monitoring devices are thus preferable.
According to a first device configuration, the said sensor of the said control means are two distinct elements of the food temperature monitoring device, these two elements being connected together via a wireless electromagnetic connection, such as the sensors described in the documents U.S. Pat. No. 4,377,733 and U.S. Pat. No. 4,475,024.
These sensors are energised by external electromagnetic energy sources.
Furthermore these electromagnetic sources must be located near to the sensor so as to avoid too great a dissipation of the electromagnetic energy during its transmission.
And the volume taken up by these electromagnetic sources reduces the available space around the food, which could pose encumbrance problems if this space is restricted as in, for example, the case of the inside of ovens or freezers, whilst making the device all the more complex through the addition of another element.
Hence the documents JP 57-082628 and U.S. Pat. No. 3,582,921 propose wireless sensors using electromagnetic transmission, operating either autonomously or semi-autonomously.
According to the first of these documents, a rechargeable battery is placed in the sensor.
According to the second document, a Nickel-Cadmium electric cell is provided in the sensor.
According to a second configuration of a food temperature monitoring device, the sensor and the control means are interdependent and thus form a unique element, such as described, for example, in the document WO 90/11497.
This temperature monitoring device is autonomous as it operates via an electric cell.
Once the thermal data has been sent by the sensor, the control means sets off a light indicator which informs the user of an excess in temperature at the centre of the food.
However, this display medium offers restrictions relative to visualisation, notably when the food is placed in an enclosed area without windows or even an opaque window, such as in some ovens or cold rooms, as visualisation then requires an opening of the enclosed area which could provoke technical problems (contamination, sudden changes in temperature, etc.).
Generally speaking, each of the sensors presented in the aforementioned documents has a long tapered part comprising at its end a temperature transducer, and a case part distant from the transducer for the protection of the electric circuit and of any eventual battery found therein.
The long tapered part enables the penetration of the transducer which it comprises into the food in order to capture the temperature, preferably at the centre, whilst preventing the electrical parts contained in the case from coming into contact with the food, as the latter could contaminate it, as well as bringing heat or cold likely to disturb its proper functioning.
However, the said temperature monitoring devices are designed to operate in microwave ovens (in which the heat is mainly around the piece of food), in moderately hot environments, at room temperature or in moderately cold environments.
Indeed, the electrical parts needed to operate the transducers of these devices are not designed to resist high temperatures such as those attainable in convection or radiant ovens (200° C. to 300° C.), nor, for some, at very low temperatures such as those attainable in freezers (between −30° C. and −40° C.).